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Biochemistry, TCA Cycle
Terms in this set (24)
The TCA cycle is also known as...
a) ATP cycle
b) Gibbs cycle
c) Jacobson cycle
d) Krebs cycle
e) Nernst cycle
Krebs cycle (aka citric acid cycle)
Which of the following statements about acetyl CoA entering the TCA cycle is correct?
a) one carbon atom and the electrons associated with it leave the TCA cycle as CO2, NADH or FAD(2H) within the same turn of the cycle
b) one carbon ataom and the electrons associated with it leve the TCA cycle as CO2, NADH or FAD(2H) within the next turn of the cycle
c) two carbon atoms and the electrons associated with them leave the TCA cycle as CO2, NADH or FAD(2H) within the same turn of the cycle
d) two carbon atoms and the electrons associated with them leave the TCA cycle as CO2, NADH or FAD(2H) within the next turn of the cycle
e) none of the above
The TCA cycle requres which of the following cofactors?
a) coenzyme A
a, b, c, d, e
Which of the following enzyme(s) reside(s) in the inner mitochondria membrane?
a) ATP synthase
b) a-ketoglutarate dehydrogenase
d) malate dehydrogenase
e) succinate dehydrogenase
The 'delta'G of acetyl CoA is 228 kcal/mol; each mol of acetyl CoA can generate 3molees of NADH ('delta' G = 53 kcal/mol), 1 mole of FAD(2H) ('delta' G = 41 kcal/mol) and 1 mole of GTP (=ATP, 'delta' G = 7.3 kcal/mol). What is the approximate energy transformation efficiency from acetyl CoA to ATPs?
Vitamin thiamine pyrophosphate (tPP) is a cofactor of several enzymes including pyruvate dehydrogenase and a-ketoglutarate dehydrogenase. Thiamine deficiency can result in lactic acidemia and Leigh disease in general. Which of the following is a major cause of thiamine deficiency besides inherited genetic mutation?
b) excessive exercise
c) nicotine addiction
The TCA cycle is regulated mainly by which of the following factors to achieve an ATP homeostasis?
a) ratio of ADP/ATP
b) ratio of ATP/NAD+
c) ratio of NAD+/NADH
d) ratio of ADP/Ca2+
e) ratio of ATP/NADH
Which of the following statements about metabolic pathway regulation is/are correct?
a) feedback regulation is common
b) regulation may occur by compartmentation
c) regulation ensures optimal system functioning
d) regulation often occurs at the last step of a pathway
e) regulation often occurs at the fastest step of a pathway
a, b, c
What is the major substrate for the TCA cycle?
acetyl CoA (acetyl coenzyme A)
What is the net reaction of the TCA cycle?
Acetyl CoA + 3NAD+ + FAD + GDP + Pi + 2H2O --> 2CO2 + CoASH + 3 NADH + 3H+ + FAD(2H) + GTP
Give a summary of the TCA cycle
Acetyl CoA -citrate synthase-> Citrate -aconitase-> Isocitrate - isocitrate dehydrogenase-> a-ketoglutarate -a ketoglutarate dehydrogenase-> Succinyl CoA -succinate thiokinase-> Succinate -succinate dehydrogenase-> Fumarate -fumarase-> Malate -malate dehydrogenase-> Oxaloacetate --> Acetyl CoA
What fuels do the acetyl group come from?
Fatty acid (palmitate), ketone body (acetoacetate), sugar (glucose), pyruvate, amino acid (alanine), ethanol
How many electrons does Acetyl CoA have to donate?
Where in the TCA cycle does oxidation take place?
NAD+ --> NADH + H+
*isocitrate to a-ketoglutarate
*a-ketoglutarate to succinyl CoA
*malate to oxaloacetate
FAD --> FAD(2H)
*succinate to fumarate
When does recycling of the high-energy thioester bond of acetyl-CoA occur in the TCA cycle?
Acetyl CoA --> Citrate
Succinyl CoA --> Succinate
When is GDP converted to GTP in the TCA cycle?
Succinyl CoA --> Succinate
Describe the overall efficiency of the TCA cycle.
-The reactions are extremely efficient in converting energy in the chemical bonds of the acetyl group to other forms.
-total amount of energy available from the acetyl group is 228 kcal/mol
What is the energy yield of the TCA cycle?
3 NADH 3*53 = 159
1 FAD(2H) 41
1 GTP 7
total = 207
What are the two major messengers that feed information on the rate of ATP utilization back to the TCA cycle?
-phosphorylation state of ATP
-reduction state of NAD+
What are the major regulatory interactions in the TCA cycle?
-regulation of citrate synthase: controlled principally by the concentration of oxaloacetate and citrate
-allosteric regulation of isocitrate dehydrogenase: one of the rate limiting steps; allosterivally activated by ADP and inhibited by NADH
-regulation of a-ketoglutarate: inhibited by NADH and succinyl-CoA and may also be inhibitedby GTP
What is the function of the regulation of the TCA cycle
-ensures that NDAH is generated fast enough to maintain ATP homeostasis
-regulates the concentration of TCA cycle intermediates
What is an anaplerotic reaction?
pathways or reactions that replenish the intermediates of the TCA cycle
What TCA Cycle intermediates are precursors and for what?
citrate --> FA synthesis
a-ketoglutarate --> AA synthesis, neurotransmitter
succinyl CoA --> heme synthesis
malate --> gluconeogenesis
oxaloacetate --> AA synthesis
What are the major anaplerotic pathways of the TCA cycle
-pyruvate to oxaloacetate
-propionyl CoA to succinyl CoA
glutamate to a-ketoglutarate
AA to fumarate
aspartate to oxaloacetate
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